Researcher gets to root of plant health

Plant pathologist Bob Linderman has devoted his career to helping plants naturally ward off pathogens.Now retired from USDA, Linderman runs a company, Plant Health, that provides research and consulting services to farmers.

Bob Linderman of Corvallis, Ore., grows mycorrhizal inoculum that is used to build plant health underground. He is the owner of Plant Health, a research and consulting firm, and Santiam Organics.

Mycorrhizal fungi are like underground “quarterbacks” that coordinate the activities of beneficial organisms in the soil, plant pathologist Bob Linderman says.

Their role is crucial in a crop’s offense — extracting water and nutrients — as well as its defense: fighting off pathogens, he said.

The fungus establishes a symbiotic relationship with the plant, living within its roots and expanding their reach to nooks and crannies in the soil that would otherwise be unreachable.

“It’s the interface between the plant and the soil,” Linderman said. “The biomass of the fungus is outstandingly large. It’s basically mining the soil.”

Linderman first became began studying mycorrhizal fungi early in his 40-year career with the USDA’s Agricultural Research Service, while looking for biological controls against plant diseases.

“I became interested in all things that happen around the roots,” he said.

Now retired from USDA, Linderman runs a company, Plant Health, that provides research and consulting services to farmers. He also manufactures the inoculum for mycorrhizal fungi through a sister company, Santiam Organics.

To produce the inoculum, the fungus is grown in a proprietary soil medium in plastic-lined bins. A crop like Sudan grass is also planted in the bins, because the fungi won’t grow without access to roots.

“You can’t grow them in a test tube,” Linderman said.

It usually requires four to five months for the mycorrhizal fungi to fully pervade the bins, at which point the fungus, medium and roots are granulated. The mixture is then bagged and is ready to use for inoculating crops with the fungus.

The benefits for mycorrhizal fungi are particularly noticeable in crops like onions or grape vines, which have coarse or limited root systems.

The fungus not only acts as an extended root system for the plant, increasing access to nutrients and water, it also improves the crop’s ability to tolerate drought.

“When mycorrhizae form, they change the physiology of the plant,” Linderman said.

The fungus also orchestrates the actions of other organisms, like “antagonistic” bacteria that help plants fight off pathogens.

“That should result in natural disease suppression,” he said. “I don’t want that disease to get a chance to happen.”

Phosphorous fertilizer has a tendency to bind to certain soils, like those rich in iron, making the nutrient less available to the plant.

“It’s not really mobile. It doesn’t move in the soil,” Linderman said. “Now you have to do something to dissolve that bond to get at the phosphorous or the iron.”

Bacteria that live on the mycorrhizal fungus create acids that break these bonds, freeing up the nutrients for the fungus to absorb.

“Once it gets to the fungus, it will go to the plant,” Linderman said.

The ability of mycorrhizal fungi to capture nutrients is useful for nursery plants grown in containers, which are prone to leaking fertilizers, he said.

“The dynamics of potting mix are different than the dynamics of soil,” Linderman said.

The company produces three distinct types of the fungus inoculum that form symbiotic relationships with different kinds of plants.

Endomycorrhizae, the most predominant type, will work with most crops.

Ectomycorrhizae form on the roots of pines, firs, spruces and oaks, while ericoid mycorrhizae are associated with blueberries, rhododendrons and cranberries.

While the fungi exist naturally in the soil, it can take a long time for plant roots to reach them, Linderman said.

Mycorrhizal inoculum, meanwhile, can be applied in-furrow during seed planting, or poured into holes when trees and shrubs are planted, ensuring quicker access to the fungi.

“I want to deliver them right from the get-go,” he said.

Bob Linderman

Occupation: Owner of Plant Health, a research and consulting firm, and Santiam Organics, which makes mycorrhizal fungi inoculum.

Age: 74

Education: Doctorate in plant pathology from the University of California-Berkeley, 1967.